1. Field of the Invention
The present invention relates to fabrication of a semiconductor device and more particularly, to a method of filling a contact hole of a semiconductor device using a dry cleaning process, and to a method of removing a damaged layer resulting from a prior dry etching process.
2. Description of Related Art
As integration density of semiconductor devices increases, cleaning processes therefor become increasingly important. For instance, following a dry etching process for forming a contact hole, it is important that a proper process of cleaning the surface of a semiconductor substrate exposed by the contact hole or the sidewalls thereof prior to a process for filling the contact hole is utilized. Dry etching for patterning is performed in such a way that reactive ions contained in plasma are accelerated using a voltage difference to etch material layers and the like on a semiconductor substrate. Such dry etching process has increased in popularity as the feature sizes of patterns applied to a semiconductor device become more minute. However, such etching process can also induce an ion bombardment effect which in turn results in lattice defect or distortion with regard to the semiconductor substrate underlying the patterned material layer or polycrystalline silicon (polysilicon). Due to the lattice defect or distortion, a damaged layer is formed on a semiconductor substrate exposed by the dry etch. The existence of the damaged layer thus formed may change the electrical properties of the substrate, for example, deteriorate the electrical conductivity.
In order to remove the damaged layer or to compensate for the degradation of electrical properties caused thereby, the following methods are being used. For example, an annealing process or ion implantation process, i.e., plug implantation preceded by formation of an electrically conductive material layer such as a plug with which to fill the contact hole is performed to compensate for the degradation of the electrical properties. Following a dry etching process, in an ashing process for removing a photoresist pattern which acts as an etching mask during a dry etching process, a method of removing an oxide layer created by oxidation of a semiconductor substrate surface by a wet etch can be used. Further, prior to a process of forming a barrier layer below an electrically conductive layer for filling a contact hole, a wet cleaning process or the like can be utilized to prevent degradation of the electrical characteristics of a semiconductor device.
There are disadvantages among the above methods. For example, the annealing process and plug implantation are complicated as well as costly. When a dielectric layer on which a contact hole is formed is made of various kinds of insulating materials having a different wet etch rate, a wet cleaning process may cause defects in the profile of contact hole sidewalls such as embossment. Further, the wet cleaning process is performed independently in a system separated from a vapor deposition system for depositing an electrically conductive material. For example, a cleaned semiconductor substrate is transferred to a single wafer type vapor deposition system, after a wet cleaning process is conducted in a batch type cleaning system such as a wet station. During such transfer, the semiconductor substrate cleaned above will be exposed to the atmosphere, resulting in contamination such as formation of a spontaneous oxide layer or absorption of contaminants. The spontaneous oxide layer and the like can significantly reduce electrical conductivity in a semiconductor device.
To solve the above problems, it is an objective of the present invention to provide a method of filling a contact hole of a semiconductor device preceded by a dry cleaning process for removing a damaged layer or spontaneous oxide layer formed on a semiconductor substrate or electrically conductive layer exposed by a dry etching process, in situ, thereby preventing the degradation of an electrical feature resulting from recontamination.
A method according to the present invention includes forming a dielectric layer on an underlying material layer, performing a dry etching process for patterning the dielectric layer to form a contact hole exposing the underlying material layer, and performing a dry cleaning process for removing a damaged layer resulting from the contact hole formation by providing the underlying material layer with plasma excited from source gas. The source gas preferably includes oxidative gas and oxide reactive gas.
The dry cleaning preferably includes the use of plasma excited from the source gas comprised of an oxidative gas such as oxygen and a fluoride gas such as trifluoronitrogen. Helium and argon gases can be further included in the source gas. The plasma is further preferably excited from the source gas by microwaves and provided to the underlying material layer by downflowing. At this stage, it is preferable to avoid a process for accelerating the plasma upon application of a voltage difference.
The dry cleaning further includes removing the spontaneous oxide layer, created from removing the damaged layer, by providing an oxide reactive gas to the underlying material layer in which the damaged layer is eliminated. In this case, the oxide reactive gas such as trifluoronitrogen gas is provided to the spontaneous oxide layer together with a hydrogen plasma which can be excited by microwaves and provided thereto by downflowing.
For a subsequent process, the present invention includes the formation of an electrically conductive layer with which to fill the contact hole. The formation of the electrically conductive layer is performed in a separate chamber clustered by being connected sequentially to a chamber for performing the dry cleaning process to thereby prevent the exposed underlying material layer inside the dry cleaned contact hole from being exposed to a source of contamination.
According to the present invention, a damaged layer resulting from dry etching for forming a contact hole can be removed and recontamination of the cleaned inside of a contact hole can be prevented, thereby avoiding increased contact resistance between an electrically conductive layer with which to fill the contact hole and an underlying material layer.